1. Field of the Invention
The present invention relates to a fail-safe device for an electronic throttle control system applied to a vehicle provided with an electronic throttle controller for electrically driving a throttle valve.
2. Description of the Related Art
Conventionally, an electronic throttle controller for an automobile engine has been developed with which electric signals are communicated between an accelerator and a throttle valve. In such an electronic throttle controller, there is no mechanical connection between the accelerator and the throttle valve. A target throttle opening degree is set by a computer based on the amount of operation of the accelerator (accelerator opening degree) and various other parameters, and the throttle valve is controlled accordingly.
Therefore, when the accelerator is not operated, that is, during idle operation where the accelerator opening degree is equal to or less than a small predetermined value, the electronic throttle controller can control the idle speed while making fine adjustment of the throttle valve. Further, such an electronic throttle controller can set the target throttle opening degree so as to correct the accelerator opening degree (operation by the driver) according to the driving condition of the vehicle and the operating condition of the engine. Therefore, with control of the throttle based on the thus obtained target throttle opening degree, the electric throttle controller can materialize engine operation with a good feeling.
On the other hand, an electronically-controlled fuel injector is generally in practical use. Based on various sensors and parameters indicating the driving condition of the vehicle and the operating condition of the engine, such an electronically-controlled fuel injector can, through a computer, arbitrarily control a target air-fuel ratio and timing of ignition in a stroke for compressing and exploding an air-fuel mixture inside the cylinder (target ignition timing). These features can be utilized both for improvement in the fuel efficiency performance of the engine and for improvement in output performance.
A system where the electronic throttle controller described above is applied to the aforementioned electronically-controlled fuel injector has recently become practical. More specifically, since the electronic throttle controller can control the throttle valve opening degree independently of the accelerator opening degree, it can supply more air to a combustion chamber than an amount corresponding to the accelerator opening degree, and thus, when the engine load is increased, for example, a required amount of air can be supplied to the combustion chamber even if the accelerator opening degree is small.
When such an electronic throttle controller is adopted, it is necessary to prepare emergency protection on the control side as a countermeasure against abnormality in each of sensors being a constituent of the electronic throttle controller or the system. As one such counter measure, a configuration can be considered where a plurality of accelerator position sensors (APSs) and a plurality of throttle position sensors (TPSs) as sensors each being a constituent of the electronic throttle controller are provided.
More particularly, double sensors are provided such that, when one of the sensors is in failure, the other of the sensors is used to electronically control the throttle. By providing the electronic throttle controller with such a double control system, the electronic throttle controller can exert fail-safe function, and thus, the safety and the reliability of the electronic throttle controller can be enhanced.
When one sensor of the double sensor system of the electronic throttle controller is in failure, the abnormality is decided and determined, and, at the same time, with fail-safe control which is set in advance, the safety when the electronic throttle controller is in failure is secured, and a warning light provided in an instrument panel is turned on to inform the driver of the abnormality in the sensor or the like.
However, when an actuator for electrically driving the electronic throttle controller or throttle valve, or a sensor being a constituent of the system is in failure; or when momentary abnormality (temporary abnormality) arises in which the state returns to a normal state before the time when a computer decides that a sensor being a constituent of the electronic throttle controller or electronic throttle control system is in failure, the rotational speed of the engine may unexpectedly increase until the computer determines the abnormality, and, due to the unexpected event, the driver may make a mistake in driving.
Causes of abnormal modes of the sensors each being a constituent of the electronic throttle controller and the electronic throttle control system include abnormality in the actuator for driving the throttle valve to open and close, abnormality in the accelerator position sensor and the throttle position sensor themselves, abnormality in a harness connecting the sensors to the computer, abnormality in a connector, abnormality in a sensor power source system, and a poor contact of a harness of the sensor power source system.
For example, during idle operation where the accelerator is not operated, if the actuator for driving the throttle valve to open and close is in failure, and is momentarily operated to open the throttle valve before the time when the computer decides that abnormality is caused, the intake air amount of the engine may be increased to unexpectedly increase the rotational speed of the engine against the driver""s will.
As described above, the target throttle opening degree is set according to the accelerator opening degree and the set various parameters. However, during idle operation where the accelerator is not operated or when the accelerator opening degree is small, if a sensor value is increased due to an abnormal mode described above for a time period until the computer decides that abnormality is caused, the target throttle opening degree may be calculated to the increase side accordingly, the throttle valve may be operated to the open side, the intake air amount of the engine maybe increased, and thus, the rotational speed of the engine may be unexpectedly increased against the driver""s will.
In this way, when the actuator for electrically driving the electronic throttle controller or throttle valve, or a sensor being a constituent of the system is in failure, the rotational speed of the engine may be unexpectedly increased for a time period until the computer decides that abnormality is caused. Thus, provision of means for avoiding this situation is a problem to be solved.
It is to be noted that, in the related art, technology is disclosed with which the safety of a vehicle is secured after deciding that abnormality is caused in an actuator for electrically driving an electronic throttle controller or a throttle valve, or a sensor being a constituent of the system, but the technology does not solve the above-described problem.
The present invention has been made to solve the above-described problem, and an object of the invention is therefore to obtain a fail-safe device for an electronic throttle control system capable of preventing unexpected increase in the rotational speed of an engine even when, in a vehicle provided with an electronic throttle controller, an actuator for electrically driving the electronic throttle controller or a throttle valve, or a sensor being a constituent of the system is in failure.
A fail-safe device for an electronic throttle control system according to the present invention includes an intake air amount sensor for detecting an intake air amount to an engine, a throttle position sensor for detecting a throttle opening degree of an electronic throttle controller, the electronic throttle controller controlling a throttle valve based on an amount of pressing down on an accelerator, an accelerator position sensor for detecting an accelerator opening degree as an amount of pressing down on the accelerator, an intake air amount control means for controlling the intake air amount to the engine, a target air-fuel ratio control means for controlling a fuel injection amount to be supplied to the engine and a target ignition timing control means for controlling ignition timing of air-fuel mixture inside a cylinder of the engine.
Also, the device includes an electronic throttle control system abnormality warning means for deciding, when a first requirement and a second requirement are satisfied based on the output of the intake air amount sensor, the throttle position sensor, and the accelerator position sensor, that the electronic throttle controller is in failure, and prior to warning of the abnormality of the electronic throttle controller, controlling the intake air amount control means, the target air-fuel ratio control means, and the target ignition timing control means.
As a result, the device can prevent in advance the rotational speed of the engine from unexpectedly increasing and the safety of the vehicle can be enhanced.